Flesh out CSSPropDefinition

[NickGerleman]

Summary:

1. Add "initial" values, and whether the prop should be inherited (currently only applies to direction).
2. Add some more border properties that we can replicate with the current data types we support, that are part of valid CSS. These are in ViewProps today instead of YogaStylableProps, but style computation can read both at once.

Changelog: [Internal]

Differential Revision: D53537101